June 27, 2014

A Glimpse Into The World Of Electric Asteroids

Space appears to be an endless vacuum void of sound, but it’s not. Electric activity not visible to the naked eye emerges from asteroids drifting through space, and NASA is now in the process of sending astronauts to an asteroid to explore its electrical environment.

Solar winds from the sun travel through space about a million miles per hour and surround all objects in the solar system. Magnetic fields are carried within these winds that collide with the magnetic fields around the other objects, discharging particles, sending electric currents millions of miles per hour, creating magnetic storms that could interrupt and damage satellites and power grids.

Space objects such as the moon and asteroids that contain an airless atmosphere, are hit by the sunlight’s negatively charged electrons producing an electrical charge on sunlit areas of these objects. The solar wind is an electrically charged plasma where matter is torn apart into electrons - which are light - and positively charged ions -which are thousands of times heavier.

The sunlit areas become positively charged and the shaded areas become negatively charged when the electrons within the solar wind flow ahead of the ions to fill voids that are created as the solar wind passes. The Earth’s surface is protected from the effects of this action by our magnetic field. However, objects without a strong magnetic field like small asteroids have no protection from the electrical activity in space.

Researchers, funded by the Solar System Exploration Research Virtual Institute (SSERVI) have developed a computer model to predict and visualize the interaction between solar wind, solar radiation and the surface of asteroids.

“Our model is the first to provide detailed, two-dimensional views of the complex interaction between solar activity and small objects like asteroids, using an adaptive computational technique that makes these simulations highly efficient,” said Michael Zimmerman, project lead at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland.

Previous models were less efficient because they didn’t produce data equally to all areas of the asteroid. The new model continually adapts the plasma to areas with lots of complex activity and less to areas that are simpler.

“Our model can calculate a solar activity-asteroid interaction in a few days. It would probably take a few weeks – or a supercomputer – for a grid-type model to do the same at high resolution,” Zimmerman said who is the lead author of a paper published in the journal Icarus.

The team plans to apply the model to see if there are any potential hazards to human explorers on the asteroids and the electrical activity on them.

“For example, understanding the electrical environment around an asteroid could help identify locations where astronauts can safely make first contact with the object. If an astronaut is tethered to a spacecraft that is in sunlight and positively charged, and touches a negatively charged asteroid surface in shadow, there could be an unexpected current flow between the two systems upon contact. We simply can't speculate on the nature of that current without this model,” said co-author William Farrell of NASA's Goddard Space Flight Center in Greenbelt, Maryland.

The model also can predict interactions between an asteroid and the spacecraft itself. “One of the reasons we're visiting asteroids is because they are relatively pristine remnants from the formation of the solar system, so they give clues as to how the planets formed and life originated. However, spacecraft release gases (like water) that ionize, and these spacecraft-emitted ions likely will contaminate the surfaces of the asteroids we want to study. This new asteroid model will allow us to estimate the degree of ion collection and contamination over various regions,” Farrell added.

The model shows that the wind flow on a smaller asteroid will display some of the same activity observed on the moon. For example, a well-developed electron cloud will form on the sunlit area of an asteroid when hit by the solar wind, while a low density supersonic wake flows behind the object. These were computer models and will have to be verified by actual measurements on future missions to asteroids, according to the researchers.

“Eventually, we also plan to expand the capability of the model by making predictions and visualizations in three dimensions, as well as adding the capability to simulate electrically conductive exploration infrastructure as well as magnetic field effects,” says Zimmerman.